I think the advantage of WASAPI exclusive over ASIO is that all sound cards, especially the built-in ones that come with computers these days, support WASAPI (on Windows 7 of course). Most consumers don’t have ASIO-compatible sound cards, and most of them aren’t going to install ASIO4ALL. So if you’re developing low-latency audio software for average consumers, which I am, WASAPI exclusive is a good compromise, even though the latency is a tad higher than ASIO (as TheVinn said, it’s usually around ~1ms for ASIO, and ~3ms for WASAPI exclusive).
Anyway I’m putting my vote in for WASAPI exclusive support. I saw the const bool in WASAPIAudioIODeviceType::createDevice, but when I set it to true, it didn’t work (it couldn’t auto-determine the proper WAVEFORMATEX).